In a process of separating materials using reverse osmosis, materials dissociated in a solution are separated from a solvent by a selective film such as a precision filtration membrane, an ultrafiltration membrane, or a reverse osmosis membrane. A reverse osmosis membrane, a type of semipermeable membrane, may remove salts from brackish water, sea water and the like, using a principle of causing a solution and a solute to be separated in predetermined directions when an aqueous solution having salts dissolved therein is pressurized in one direction, thereby being used to desalinate a great quantity of water for industrial, agricultural, domestic and other purposes, into relatively lower-salinity water.
More specifically, brackish and sea water desalination processes using the reverse osmosis membrane refer to processes of filtering salts, ions or the like, dissolved in an aqueous solution through a reverse osmosis membrane and allowing refined water to pass through the membrane, when the reverse osmosis membrane passes through the aqueous solution having salts, ions or the like dissolved therein while pressure is applied to the aqueous solution. At this time, the level of applied pressure needs to be greater than that of osmotic pressure. Accordingly, osmotic pressure is higher in accordance with an increase in salinity and consequently, the pressure required to be applied to supply water may be increased, causing the depletion of a greater amount of energy.
Thus, in order to desalinate brackish water, sea water and the like, containing a great deal of salts, a reverse osmosis membrane needs to have properties allowing a great quantity of water to pass therethrough, even at relatively low pressure, that is, high permeate flux properties, as well as having good salt removal capabilities.
As described above, in order to increase a salt rejection rate and permeate flux performance of the reverse osmosis membrane, various patent documents according to the related art provide reverse osmosis membranes having an improved salt rejection rate and permeate flux and methods of manufacturing the same. For example, Korean Patent Laid-Open Publication No. 1999-0070132 (Sep. 15, 1999) is characterized by performing interfacial polymerization and then, carrying out an additional treatment process, Korean Patent Laid-Open Publication No. 1999-0070134 (Sep. 15, 1999) is characterized by using a mixed organic solvent, and Korean Patent Laid-Open Publication No. 1999-0019008 (Mar. 15, 1999) is characterized by adding an additive to an organic solvent.
However, in the case in which an additional process is undertaken before or after a porous support is immersed in a polyfunctional amine solution, a complex process is caused and costs required therefor are increased. In addition, in the case in which a mixed organic solvent is used or an additive is added to an organic solvent, the reverse osmosis membrane has limitations in terms of the salt rejection rate and the permeate flux thereof. In particular, according to the related art, it may be difficult to obtain significant effects in terms of hydrophilic properties and uniformity in hydrophilicity on a surface of a polyamide active layer in the reverse osmosis membrane.
Thus, the present invention is provided by the applicant thereof as a result of repeated research in order to develop a reverse osmosis membrane having improved degrees of compactness and uniformity in a polyamide active layer surface, as well as having an improved permeate flux and salt rejection rate, through a further effective, simple method.